JP5427796B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device that enables a vehicle to turn with a light steering force of the steering wheel when a steering force applied to a steering wheel by an operator is transmitted to the wheel through a steering system.

  A steering force applied to the steering wheel by the operator is detected by a torque sensor provided on a steering shaft connected to the steering wheel. Based on the steering force (steering torque) detected by the torque sensor, in the electric power steering device, the control device drives an electric motor (also simply referred to as a motor), and assist torque (auxiliary torque) generated by the motor. ) Is transmitted to the steering shaft (steering system) via a worm gear reduction mechanism or the like, thereby reducing the steering force of the steering wheel by the operator.

  In this case, as the torque sensor, as shown in Patent Document 1 and Patent Document 2, the input shaft and the output shaft are connected by a torsion bar, and a core that engages the input shaft and the output shaft is provided. When torque acts between the input output shafts, the core is displaced, and the displacement of the core is electrically detected by a detection coil, or as shown in Patent Document 3 and Patent Document 4, It is known that a detection coil for covering a magnetostrictive film and detecting a magnetic characteristic change of the magnetostrictive film is provided so that torque applied to the steering shaft is electrically detected by the detection coil.

  In Patent Document 5, when the torque sensor fails, when the vehicle speed is equal to or higher than a predetermined speed, the assist of the steering force by the motor is canceled and manual steering is performed. When the vehicle speed is equal to or lower than the predetermined speed, the steering angle is A technique has been proposed in which a motor is controlled according to a steering angular velocity calculated from the output of a sensor.

Japanese Patent No. 3055752 Japanese Patent No. 2830992 Japanese Patent No. 3964414 Japanese Patent No. 4057552 Japanese Patent Publication No. 6-96389

  Conventionally, when a torque sensor that detects steering torque fails, as described in Patent Document 5, the motor is controlled in accordance with the steering angular velocity calculated from the output of the steering angle sensor.

  However, in a vehicle to which the steering angle sensor is not added, when the torque sensor fails and the steering torque cannot be detected, the assist of the steering force by the motor must be released.

  The present invention has been made in consideration of such problems. Even when the torque sensor fails and the torque torque cannot be detected by the torque sensor, the steering assist force by the motor is changed in the cutting direction and An object of the present invention is to provide an electric power steering apparatus that can be applied in both directions of the switchback direction, and in particular, can easily return an operator such as a steering wheel to the vicinity of the neutral position at the time of switchback.

The electric power steering apparatus according to the present invention is
An operator that the driver operates to steer the vehicle;
A torque detector for detecting torque generated in the steering system of the vehicle;
A vehicle speed detector for detecting the vehicle speed of the vehicle;
A motor for applying assist torque to the rotating shaft of the steering system;
A rotation angle detector for detecting a rotation angle of the steering system;
A motor control unit for controlling a current for driving the motor based on the torque detected by the torque detection unit;
An electric power steering apparatus comprising:
An abnormality detection unit for detecting whether an abnormality has occurred in the torque detection unit;
A storage unit that stores, as a characteristic, a relationship between the rotation angle detected by the rotation angle detection unit and the current that drives the motor, and the motor control unit includes:
When an abnormality of the torque detection unit is detected by the abnormality detection unit, a switchback angle remains at the time of switchback in which the steering angle (also referred to as an operation angle) of the operation element changes in a direction approaching a neutral position . In the state, when the assist current in the cutting direction becomes close to zero value, the rotation angle detected by the rotation angle detection unit is used as a reference angle to detect the return rotation angle,
The motor is driven based on the switching back rotation angle and the characteristic.

  According to the present invention, when the assist current in the cutting direction becomes close to the zero value with the switchback angle remaining, the switchback rotation angle is detected with the rotation angle detected by the rotation angle detector as the reference angle. Since the motor is driven based on the return rotation angle and the characteristics, the operation angle of the operator can be assisted in the direction approaching the neutral position, and the operator by the driver on the return side The steering force can be reduced and the operator can be easily returned to the vicinity of the neutral position.

  In this case, the driving of the motor at the time of switching back may be effective when the vehicle speed is equal to or lower than a predetermined vehicle speed.

  According to the present invention, when the operating element is operated in the return direction with the return angle remaining when the vehicle speed is equal to or lower than the predetermined vehicle speed, the weak SAT (self-aligning torque) is taken into consideration. Since the assist force is sometimes applied, the driver's steering force on the switchback side can be reduced.

  In addition, it is preferable to multiply the drive current of the motor at the time of the switch back by a predetermined coefficient corresponding to the steering performance of the vehicle.

  In other words, the steering performance of the vehicle changes depending on the magnitude of the load (vehicle front axle load) for each individual vehicle. Therefore, by multiplying the driving current of the motor by a coefficient corresponding to the steering performance of the vehicle, the steering of the vehicle is performed. Optimum assistance according to the nature becomes possible.

  The assist current becomes substantially zero at the neutral position by avoiding over-assist by making the motor current smaller as the steering angle of the operating element corresponding to the return angle approaches the neutral position. Can do.

  Further, when the steering angle of the operation element reaches a neutral position at the time of the switch back, the assist in the subsequent cut direction can be appropriately performed by resetting the switch back rotation angle.

  According to the present invention, when the abnormality of the torque detection unit is detected by the abnormality detection unit, the motor is driven based on the characteristics of the current that drives the motor with respect to the rotation angle detected by the rotation angle detection unit. Therefore, for example, even when the torque sensor fails and the steering torque cannot be detected by the torque sensor, the steering assist force can be applied. Then, when the assist current in the cutting direction becomes close to a zero value with the switchback angle remaining, the switchback rotation angle is detected using the rotation angle detected by the rotation angle detector as a reference angle, and the switchover angle is detected. Since the motor is driven based on the return rotation angle and the characteristics, the operation angle of the operator can be assisted in the direction approaching the neutral position, and the steering force of the operator on the return side by the driver And the operator can be easily returned to the vicinity of the neutral position.

1 is an overall schematic configuration diagram of an electric power steering apparatus according to an embodiment and first to third examples. FIG. 2 is a connection diagram in an ECU in the electric power steering apparatus of FIG. 1 example; It is a flowchart provided for description of a steering angle estimation process and a current fade process. 4A is an explanatory diagram of a base assist current characteristic referred to in the normal assist process, and FIG. 4B is an explanatory diagram of a base assist current characteristic referred to in the abnormal assist process. It is explanatory drawing of a current fade characteristic. It is explanatory drawing of the continuous steering time reduction characteristic. It is a flowchart with which description of the interruption process of the steering return switchback current fade process which concerns on 1st Example is provided. It is a flowchart with which description of the resumption process of the interruption process of the switchback current fade process at the time of a steering maintenance which concerns on 1st Example is provided. It is explanatory drawing of the assist characteristic at the time of steering according to 1st Example. It is explanatory drawing of the motor rotational speed reduction ratio characteristic which concerns on 2nd Example. It is explanatory drawing of the vehicle speed ratio characteristic which concerns on 2nd Example. It is explanatory drawing of the excessive cut suppression function of the cutting direction which concerns on 2nd Example. It is a flowchart with which description of the steering force reduction process at the time of low speed travel area switchback concerning 3rd Example is carried out. It is explanatory drawing of the steering force reduction characteristic at the time of low speed travel area switchback concerning 3rd Example. It is explanatory drawing of the center ratio characteristic which concerns on 3rd Example. Schematic characteristic diagram comparing the steering force required by the driver in the conventional assist control, the steering force required by the driver in the assist control according to the present invention, and the steering force required by the driver when there is no assist control It is.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall schematic configuration diagram of an electric power steering apparatus 10 according to this embodiment mounted on a vehicle.

  FIG. 2 is a functional block diagram in an ECU (Electronic Control Unit) 22 in the electric power steering apparatus 10 of FIG.

As shown in FIG. 1, the electric power steering apparatus 10 basically steers from the steering wheel 12 (operator operated by the driver to steer the vehicle) to the steered wheels 16 via the steering shaft 14. Torque sensor which is provided on a rotating shaft of the steering system 18 and has a steering angle sensor 19 therein and detects torque Tr and steering angle (also referred to as operation angle ) θs of the rotating shaft . (Also referred to as a torque sensor and a steering angle sensor) 20, an ECU 22 that determines an assist torque Ta based on an output from the torque sensor 20, and the like, and an electric motor (hereinafter referred to as a motor) that is a brushless motor driven by the ECU 22. 24) and the output of the motor 24 is decelerated and transmitted as an assist torque Ta to the rotating shaft of the steering system 18. Provided that the reduction transmission mechanism 26. The motor 24 may be a brush motor.

  In the torque sensor 20, an input shaft 41 and an output shaft 42, each of which is a rotation shaft of the steering system 18, are connected by a torsion bar inside, and two detection coils (not shown) supported by a housing (not shown) are inserted. A known configuration is provided so as to surround a cylindrical core (not shown) engaged with the output shafts 41 and 42 (see, for example, Patent Document 1 and Patent Document 2).

  The steering angle sensor 19 has a known configuration that detects the rotation angle of the input shaft 41 as the steering angle θs (see, for example, Patent Document 1).

  The torque sensor 20 may have a known configuration using a magnetostrictive film sensor that does not use a torsion bar or a cylindrical core (see, for example, Patent Document 3 or Patent Document 4).

  Even if the torque sensor does not include the steering angle sensor 19, if a steering angle sensor for detecting the rotation angle of the steering system 18 is separately provided, for example, side slip suppression control during turning of the vehicle is performed. In a vehicle, the present invention can be applied by using the separately provided steering angle sensor.

  The torque Tr and steering angle θs signals output from the torque sensor 20 and the steering angle sensor 19 are supplied to the torque detection circuit 72 of the ECU 22 through the harness 91, and the steering angle θs is calculated as a steering angular velocity. Supplied to the unit 74.

  The steering shaft 14 includes a main steering shaft 15 integrally coupled to the steering wheel 12, each of which is a rotating shaft, an input shaft 41 coupled to the main steering shaft 15 via a universal joint 46, a rack & The output shaft 42 provided with the pinion 30 of the pinion mechanism 28 is connected.

  The input shaft 41 and the output shaft 42 are supported by bearings 48 a, 48 b and 48 c, and the pinion 30 is provided at the lower end portion of the output shaft 42. The pinion 30 meshes with the rack teeth 50a of the rack shaft 50 that can reciprocate in the vehicle width direction. The steered wheels 16 that are the left and right front wheels are connected to both ends of the rack shaft 50 via tie rods 52.

  More specifically, the steering system 18 described above includes a rack having the steering wheel 12 to the steering shaft 14 (the main steering shaft 15, the universal joint 46, the input shaft 41, the output shaft 42 provided with the pinion 30), and rack teeth 50a. The shaft 50, the tie rod 52, and the steered wheel 16 are included.

  With this configuration, a normal rack and pinion type steering operation can be performed when the steering wheel 12 is steered, and the steering wheel 12 can be operated to steer the steered wheels 16 and change the direction of the vehicle. Here, the rack shaft 50, the rack teeth 50 a, and the tie rod 52 constitute a steering mechanism in the steering system 18.

  As described above, the electric power steering apparatus 10 includes the motor 24 that supplies a steering assist force (a steering assist force, also simply referred to as an assist force) for reducing the steering force by the steering wheel 12. The worm gear 54 fixed to the rotating shaft 25 of the motor 24 meshes with a worm wheel gear 56 provided on the lower side of the bearing 48b in the intermediate portion of the output shaft 42. The worm gear 54 and the worm wheel gear 56 constitute the speed reduction transmission mechanism 26.

  A rotation angle θrm (also referred to as a motor mechanical angle) of the rotor 23 of the motor 24 that rotates integrally with the rotation shaft 25 is converted into a rotation angle θr (also referred to as a motor electrical angle) of the rotor 23 by a resolver 58 as a rotation angle detector. And is supplied to a rotor rotation angle detection circuit (functioning as a motor mechanical angle calculation circuit for calculating a motor mechanical angle θrm described later) 76 of the ECU 22 through the harness 92. The resolver 58 is a relative angle detection sensor, but a rotary encoder of an absolute angle detection sensor may be employed instead of the resolver 58. The difference between the rotation angle θrm (motor mechanical angle) and the rotation angle θr (motor electrical angle) will be described later.

  The ECU 22 is a computer including a microcomputer, a CPU (Central Processing Unit), a ROM (including EEPROM) and a RAM (Random Access Memory), and other A / D converters, D / A converters, and the like. Input / output device, a timer (timer) as a time measuring means, etc., and when the CPU reads and executes a program recorded in the ROM, various function realizing parts (function realizing means) such as a control part, Functions as an arithmetic unit, a processing unit, and the like.

  In this embodiment, the ECU 22 includes a storage unit 78 as a memory for storing various characteristics (including maps), programs, and the like, which will be described later, and includes the torque detection circuit 72, the steering angular velocity calculation unit 74, and the rotor. In addition to functioning as the rotation angle detection circuit 76, it functions as an abnormality detection unit 80, a vehicle stop state detection unit 82, a motor control unit 84, a time measuring unit 85, and the like.

  The torque detection circuit 72 is a signal corresponding to the torque Tr from the differential signal of the signal related to the torque Tr output from the two detection coils (not shown) of the torque sensor 20 through the harness 91 (for convenience of understanding, Torque Tr) is generated and supplied to the motor control unit 84.

  The rotor rotation angle detection circuit 76 calculates (detects) a rotation angle (motor mechanical angle) θrm corresponding to the rotation of the rotor 23 of the motor 24 from the rotation angle θr (motor electrical angle) supplied from the resolver 58. While supplying to the motor control part 84, it supplies to the steering angular velocity calculation part 74. FIG.

  The steering angular velocity calculation unit 74, when a steering angle (also referred to as a steering angle, steering angle, or steering angle of the steering shaft 14) θs is supplied from the steering angle sensor 19 that is operating normally, the steering angle sensor. The steering angle θs output from 19 through the harness 91 is differentiated to generate a steering angular velocity θs ′ (θs ′ = dθs / dt: d is a differential operator, t is time), and is supplied to the motor control unit 84.

  On the other hand, when an abnormality occurs in the steering angle sensor 19 or in a vehicle that is not originally provided with the steering angle sensor 19, the steering angular velocity calculation unit 74 is calculated by the rotor rotation angle detection circuit 76 based on the rotation angle θr of the resolver 58. The estimated steering angular velocity θsc ′ (θsc ′ = dθsc / dt: d is a differential operator, and t is time) is obtained by time differentiation of the estimated steering angle θsc calculated from the motor mechanical angle θrm.

  The abnormality detection unit 80 monitors the torque Tr, which is the output of the torque detection circuit 72, and the steering angle θs, which is the output of the steering angle sensor 19, so that the fusing failure between the terminal of the torque sensor 20 and the harness 91, Opening of harness 91 (disconnection of harness 91), short circuit between harnesses 91, abnormality of differential amplifier in torque detection circuit 72, for example, output is fixed at 0 volts or voltage other than 0-5 volts Is detected, the abnormality detection signal Sab is supplied to the motor control unit 84 and the steering angular velocity calculation unit 74.

  The motor control unit 84 and the vehicle stop state detection unit 82 of the ECU 22 are further supplied through the harness 94 with the output of the vehicle speed sensor 86 that detects the vehicle speed Vs from the rotation speed of the front and rear wheels or the transmission, that is, the vehicle speed Vs.

  Furthermore, the brake operation signal Sb of the parking brake 88 is supplied through the harness 95 to the vehicle stop state detection unit 82 and the motor control unit 84 of the ECU 22.

  In practice, signals such as the vehicle speed Vs and the brake operation signal Sb are supplied to the ECU 22 through an in-vehicle network such as CAN (controller area network). You may connect by what is called a point-to-point wiring system instead of an in-vehicle network.

  When the brake operation signal Sb of the parking brake 88 is detected, or when it is detected that the vehicle speed Vs has reached zero, the vehicle stop state detection unit 82 supplies the vehicle stop detection signal Sstop to the motor control unit 84. To do.

  When the motor control unit 84 determines the assist current Ia of the motor 24 corresponding to the assist torque Ta, in addition to the torque Tr and the steering angular velocity θs ′, the rotation angle (motor mechanical angle) θrm of the rotor 23 and the estimated steering angle θsc. Based on the estimated steering angular velocity θsc ′, the abnormality detection signal Sab, the vehicle speed Vs, the brake operation signal Sb, and the like, a characteristic (described later) stored in the storage unit 78 (characteristic storage unit) is referred to, and the program is executed. The assist current Ia thus determined is supplied to the stator coil of each phase of the motor 24 through the harness 93.

  The motor 24 generates an assist torque Ta corresponding to the supplied assist current Ia and applies it to the output shaft 42 through the deceleration transmission mechanism 26 to generate a steering assist force on the steering shaft 14.

  The characteristic operation of the electric power steering apparatus 10 of this embodiment that is basically configured and operates as described above will be described below with reference to flowcharts and the like.

  FIG. 3 is a flowchart for explaining the operation of the electric power steering apparatus 10 according to this embodiment. The process according to this flowchart is repeatedly executed every predetermined time.

  The ECU 22 performs a steering angle estimation process (estimated steering angle calculation process) in steps S1 to S3 regardless of whether the torque sensor 20 or the steering angle sensor 19 is abnormal.

  In step S1, the rotor rotation angle detection circuit 76 integrates the rotation angle θr (electric angle of the rotor 23) detected by the resolver 58, and calculates the motor electric angle θre.

  Next, in step S2, the rotor rotation angle detection circuit 76 multiplies the calculated motor electrical angle θre by the number of pole pairs of the resolver 58 as shown in the following equation (1) to obtain the rotor 23 (rotation shaft 25). ) Is calculated (converted to the motor mechanical angle θrm) and supplied to the motor control unit 84 and the steering angular velocity calculation unit 74.

Motor mechanical angle = motor electrical angle × resolver pole pair number θrm = θre × resolver pole pair number (1)

  Next, in step S3, the motor control unit 84 and / or the rotor rotation angle detection circuit 76 uses the calculated motor mechanical angle θrm as the steering angle (estimated steering) of the steering shaft 14 as shown in the following equation (2). Angle) Converted to θsc.

Estimated steering angle = motor mechanical angle × (ratio of rotational axis of motor 24 to rotational axis of steering system 18) = motor mechanical angle × reduction ratio of deceleration transmission mechanism 26 θsc = θrm × reduction ratio of deceleration transmission mechanism 26 (2 )

In this embodiment, the speed reduction ratio of the speed reduction transmission mechanism 26 is set to 1/20. That is, in this embodiment, 360 [deg] of the motor mechanical angle θrm is converted to 18 (= 360/20) [deg] at the estimated steering angle θsc that estimates the rotation of the steering wheel 12 (output shaft 42). The Similarly, the motor rotation speed N, which is the rotation speed of the rotor 23 of the motor 24 per second, for example, N = 2 [rps] is the rotation speed (estimated steering rotation speed) of the steering wheel 12 (output shaft 42). Nsc corresponds to Nsc = 0.1 (= 2/20) [rps].

  The estimated steering rotational speed Nsc = 0.1 [rps] of the steering wheel 12 (output shaft 42) is θsc ′ = 36 (0.1 [rps] × 360 [deg]) [ deg / s]. Therefore, the motor rotational speed N and the estimated steering angular speed (rotational angular speed) θsc ′ uniquely correspond to each other. For example, a motor rotation speed N of N = 2 [rps] corresponds to θsc ′ = 36 [deg / s] of the estimated steering angular velocity θsc ′.

  The motor rotation speed N and the estimated steering rotation speed Nsc are calculated by the motor control unit 84.

  As shown in FIG. 1, when the output shaft 42 that rotates integrally with the steering shaft 14 fixed to the steering wheel 12 rotates together with the worm wheel gear 56 that is fixed to the output shaft 42, the worm gear rotates. When the worm gear 54 is rotated, the rotating shaft 25 (rotor 23) of the motor 24 fixed to the worm gear 54 is integrally rotated, and the rotation of the rotor 23 is detected by the resolver 58. As a result, the estimated steering angle θsc obtained by estimating the steering angle θs, which is the rotation angle of the steering wheel 12, can be calculated (detected) based on the rotation angle θr by the resolver 58.

  Note that the steering angle θs and the estimated steering angle θsc are set so that the right turn of the steering wheel 12 is positive and the left rotation is negative, and the driver makes a right turn from a straight traveling state (θs = θsc = 0 [deg]). First, the steering wheel 12 is rotated to the right and cut, and then turned to the left and turned back to return to the straight traveling state. Therefore, basically, when turning right from the straight traveling state and returning to the straight traveling state, the right rotation is the cutting direction and the left rotation is the returning direction.

  On the other hand, when making a left turn from the straight traveling state (θs = θsc = 0 [deg]), first, the left turn is performed, then the right turn is performed, and then the straight traveling state is restored. Therefore, basically, when turning left from the straight traveling state and returning to the straight traveling state, the left rotation is the cutting direction, and the right rotation is the switching back direction.

  Thus, the steering angle θs (estimated steering angle θsc) when the steering wheel 12 is rotated rightward from the straight traveling state (neutral state of the steering wheel 12) becomes a positive value, and the straight traveling state (the steering wheel 12 of the steering wheel 12). The steering angle θs (estimated steering angle θsc) when the steering wheel 12 is rotated in the left direction from the neutral state is a negative value. When considering the magnitude of the angle, if there is a positive / negative sign, it is complicated. Therefore, in the following description, unless otherwise noted, a case where the vehicle turns right from the straight traveling state and returns to the straight traveling state will be described as an example (on the coordinates of the steering assist characteristic, the first quadrant). In this case, both the steering angle θs and the estimated steering angle θsc take positive values.

  In this embodiment, even if the steering angle sensor 19 and the torque sensor 20 become abnormal due to the procedure of steps S1 to S3 described above, in this embodiment, the rotor rotation is performed based on the rotation angle θr detected by the resolver 58. The estimated steering angle θsc [deg] and the estimated steering angular velocity θsc ′ [deg / s] from which the steering angle θs [deg] is estimated by the angle detection circuit 76, the steering angular velocity calculation unit 74, and the motor control unit 84 can be obtained. .

  Note that the steering assist force applied to the steering wheel 12 by rotating the motor 24 may basically be applied in the direction in which the steering angle θs or the estimated steering angle θsc is changing.

  Next, in step S4, it is detected whether or not the abnormality detection signal Sab is supplied from the abnormality detection unit 80. In step S4, when the motor control unit 84 detects the abnormality detection signal Sab related to the torque sensor 20 and the steering angle sensor 19, the motor control unit 84 executes the processing after step S5. In the torque sensor 20 with a built-in steering angle sensor 19 shown in FIG. 1, the supply of power is stopped by opening or shorting the harness 91, and the outputs of the steering angle sensor 19 and the torque sensor 20 are in an abnormal state at the same time. There are many cases.

  In step S4, when the motor control unit 84 does not detect the abnormality detection signal Sab, normal processing (normal assist processing) is performed in step S21. In this normal process, since the torque sensor 20 and the steering angle sensor 19 are normal, a conventional steering assist force application operation is performed.

  In this case, the motor control unit 84 has characteristics (base assist current characteristics) of the base assist current Ia [A] with respect to the steering torque Tr [kgfcm] with the vehicle speed Vs as a parameter shown in FIG. Alternatively, it is also referred to as a base assist characteristic.) 101 is referred (searched), and basically the base assist current Ia that increases as the vehicle speed decreases is calculated to drive the motor 24.

  On the other hand, in step S4, when the motor control unit 84 detects the abnormality detection signal Sab in which the torque sensor 20 or the like has become abnormal, the abnormality assist process in step S5 is executed.

  In step S5, the motor control unit 84 characteristics of the base assist current Ia [A] with respect to the estimated steering angle θsc shown in FIG. 4B stored in advance in the storage unit 78 (also referred to as base assist current characteristics or base assist characteristics). The base assist current Ia is calculated by referring to (searching) 102, and the motor 24 is driven based on the base assist current Ia.

  The base assist current characteristic 102 may be stored in the storage unit 78 as a map, or may be stored in the storage unit 78 using a calculation formula. When the data are stored in the storage unit 78 discretely as a map, the value between them is preferably obtained by interpolation.

  As can be seen from FIG. 4B, in the base assist current characteristic 102, the estimated steering angle θsc [deg] is a value from 0 [deg] to a dead zone corresponding steering angle θd [deg] (about 0 to 10 [deg]). In this embodiment, it is set to 10 [deg].) In the vicinity of the neutral position up to 10 [deg], Ia = 0 [A] is set (a region where the assist current Ia does not flow), and the dead zone corresponding steering angle θd [ deg] or higher, and the estimated steering angle θsc is increased in accordance with the increase of the estimated steering angle θsc (increased approximately proportionally). In the vicinity of [deg], the characteristic is set to take a constant value (the value of the base assist current Ia is saturated).

  As described above, in this embodiment, even when an abnormality is detected when the abnormality detection signal Sab is detected, the assist current Ia based on the base assist current characteristic 102 is supplied to perform predetermined steering assist control. However, the steering assist control at the time of abnormality is a provisional assist process, and various restrictions are imposed as described later.

  As described above, the electric power steering apparatus 10 according to this embodiment includes the torque sensor 20 as a torque detection unit that detects the torque Tr generated in the steering system 18 and the output shaft 42 that is the rotation axis of the steering system 18. Based on the motor 24 for applying the assist torque Ta, the resolver 58 as a rotation angle detection unit for detecting the rotation angle θr of the rotor 23 of the motor 24, and the torque Tr detected by the torque sensor 20, An electric power steering apparatus 10 that includes a motor control unit 84 that controls a drive current, and includes an abnormality detection unit 80 that detects whether or not an abnormality has occurred in the torque sensor 20 or the torque detection circuit 72, and motor control When the abnormality detection unit 80 detects an abnormality in the torque sensor 20 or the torque detection circuit 72, the unit 84 resolves the resolver 5. By calculating the motor mechanical angle θrm based on the motor electrical angle θre that is an integrated value of the rotation angle θr detected by the above, the estimated steering angle θsc is calculated {see the above formula (2)}, and this estimated steering angle θsc Referring to the base assist current characteristic 102, the base assist current Ia [A] is calculated, and the motor 24 is controlled to be driven based on the base assist current Ia.

  By controlling the drive of the motor 24 in this way, even if an abnormality in the torque sensor 20 or the torque detection circuit 72 is detected and the steering torque Tr cannot be detected by the torque sensor 20, the motor 24 A steering assist force can be applied to the steering wheel 12 by the assist torque Ta.

  When the torque sensor 20 is in a normal state, when the output of the torque sensor 20 has a substantially zero value and the detected value of the vehicle speed Vs at the vehicle speed sensor 86 is at a substantially constant speed, the resolver is The intermediate steering (neutral state) correction process for updating the stored content with the estimated steering angle θsc corresponding to the rotation angle θr as the output of 58 as a zero value (θsc = 0 [deg]) is appropriately performed.

  In addition, since the provision of the steering assist force using the rotor rotation angle detection circuit 76 is a provisional process, when the abnormality detection unit 80 detects an abnormality in the torque sensor 20 or the like, it is The operator (driver) is informed that the steering force assist process corresponding to the abnormality is being performed. Thereby, the operator (driver) can drive the vehicle to a safe place by using the assist force by the provisional electric power steering using the rotation angle θr of the rotor 23 of the motor 24.

  The assist force by the provisional electric power steering imposes various restrictions on the normal assist process in step S21 in which the torque sensor 20 and the like are in a normal state.

  As one of the restrictions, first, the current fade process in steps S6 to S9 will be described.

  FIG. 5 shows a cut-in current fade characteristic (also referred to as a cut-in current fade characteristic) 103 used for a current fade process stored in the storage unit 78, and a switch-back current fade characteristic (also referred to as a switch-back current fade characteristic). .) The example 104 is shown, and a part of the base assist current characteristic 102 of FIG. 4B is shown again. In the following, for the convenience of understanding, the characteristics of the first quadrant in FIG. 5 (the cutting direction in the right direction from 0 [deg] on the horizontal axis toward the large value in the positive direction, and 0 from the positive direction) (Characteristics related to the return direction toward a small value in the [deg] direction).

  In step S6, it is determined from the estimated steering angular velocity θsc ′ that is a differential value of the estimated steering angle θsc whether the assist current Ia is being energized and the steering wheel 12 is being turned. The estimated steering angular velocity θsc ′ is calculated by the steering angular velocity calculator 74 or the motor controller 84.

  When the cutting is in progress, the assist current Ia is determined along the cutting current fade characteristic 103 and the motor 24 is driven and controlled.

5, Oite the same estimated steering angle [theta] s c, reason for the cut current fading characteristic 103 shown by a chain line is reduced assist amount than the base assist current characteristic 102 is shown by a solid line (assist current Ia) Is to prevent excessive cutting. When the steering wheel 12 is continuously turned in the same direction, the motor control unit 84 refers to the time from the start of turning {the continuous steering time tr (in the same direction). } Is measured by the timer 85 and the ratio (referred to as a continuous steering reduction ratio or a continuous steering reduction ratio) Rc {Rc is 1 (no reduction) to 0 with reference to the continuous steering time reduction characteristic 105 shown in FIG. The values up to (assum the assist current Ia to zero) are taken. } Is calculated.

When continuous steering is detected, the assist current Ia calculated by the estimated steering angle θsc on the base assist current characteristic 102 is multiplied by the continuous steering reduction ratio Rc corresponding to the continuous steering time tr , and then As shown in the equation (3), the assist current Ia is faded (reduced).
Ia ← Ia × Rc (3)

In the equation ( 3), Ia on the right side of the equation means base assist current on the base assist current characteristic 102, and Ia on the left side means faded (reduced) base assist current on the cut-in current fade characteristic 103.

  In this example, the continuous steering reduction ratio Rc of the continuous steering time reduction characteristic 105 is such that the assist current Ia is reduced by 10% in 1 second (1 [s]). When it is detected that cutting continues in the same direction, the assist current Ia is set to zero.

Thus, in the current fading process cuts step S7, if the continuous feed steering in the same direction as the cut current fading characteristic 103 you reduce the assist amount (assist current Ia) than the base assist current characteristic 102 I try to assist.

  Further, in order to prevent over-assist current at the time of turning, when the estimated steering angle θsc is equal to or larger than the threshold steering angle θscth, the assist current Ia is limited to the allowable maximum assist current Iamax {coordinate point 106 in FIG. (See θscth, Iamax)}.

Then, in step S8, the estimated steering angular velocity θsc'(θsc' = dθsc / dt) is substantially zero value (θsc' ≒ 0 [deg / s ]), in this embodiment, the threshold steering angular Shitasc'th (absolute value ) Is, for example, a value equal to or smaller than θsc′th = 7.2 [deg / s] (converted to estimated steering rotation speed Nsc = 0.02 [rps], converted to motor rotation speed N = 0.4 [rps]). (Θsc ′ ≦ θsc′th = 7.2), and if the determination in step S8 is affirmative, in order to promote the return of the steering wheel 12 at the time of switching back, A switchback current fade process is executed.

  During execution of the switchback current fade process in step S9, the assist current Ia is determined along the switchback current fade characteristic 104 of FIG.

This switch-back current fade characteristic 104 indicates that the assist current Ia = Ia1 {coordinate point 107 (θsc1, Ia1) at the estimated steering angle θsc = θsc1 when the estimated steering angular velocity θsc ′ is equal to or less than the threshold steering angular velocity θsc′th. )}, The assist current Ia (Ia = Ia1 in the example of FIG. 5) is gradually attenuated to a zero value, for example, proportionally and automatically, in a time of about 1 second counted by the timing unit 85. At this time, in the switchback current fade characteristic 104, the estimated steering angle θsc is switched back to the left so that the steering wheel 12 (steering system 18 ) acting on the traveling vehicle is moved straight (neutral position). It depends on the force to return, so-called SAT (Self Aligning Torque).

  As described above, the steering angular velocity calculation unit 74 or the motor control unit 84 that calculates the estimated steering angular velocity θsc ′ of the output shaft 42 that is the rotation axis of the steering system 18 is provided. When the absolute value of the estimated steering angular velocity θsc ′ calculated by the calculation unit 74 is close to zero (for example, as described above, the threshold steering angular velocity θsc′th = 7.2 [deg / s]), The assist current Ia for driving the motor 24 is switched back and the current fade characteristic 104 {the gradient of this characteristic 104 changes according to the load (front axle load of the vehicle), the vehicle speed Vs, the road surface condition, and the like. }, The over-assist current can be prevented.

  Of course, when the steering angle sensor 19 attached to the torque sensor 20 or the steering angle sensor provided independently of the torque sensor 20 is in a normal state, the steering angle θs that is the output of the steering angle sensor 19 or the like. Is differentiated to calculate the steering angular velocity θs ′ and the current fade process can be performed.

  When the vehicle speed Vs [km / h] detected by the vehicle speed sensor 86 detects at least one of Vs = 0 and the brake operation signal Sb due to the operation of the parking brake 88, the vehicle stop state detection unit 82 detects The vehicle stop detection signal Sstop is supplied to the motor control unit 84. At this time, the motor control unit 84 can prevent the steering assist force from being unnecessarily applied by setting the assist current Ia to a zero value.

  When the parking brake 88 is released and the drive wheels are rotated by an engine or the like, for example, when the vehicle is lifted up at a service factory or the like and the drive wheels are idling, so-called self-steering is not achieved. As described above, the present invention includes that the assist current Ia is not supplied when the vehicle speed Vs detected by the vehicle speed sensor 86 is Vs = 0.

As described above, according to the embodiment described above, in a case where it becomes impossible to detect the steering torque Tr by the torque sensor 20 torque sensor 20 has failed also, Ri by the resolver 58 of the motor 24 detected The steering angle θs and the steering angular velocity θs ′ are estimated using the rotation angle θr of the rotor 23 of the motor 24, and the predetermined steering assist force by the motor 24 is used using the estimated steering angle θsc and the estimated steering angular velocity θsc ′. Can be granted.

[First embodiment] (Assist function during steering)
According to the above-described embodiment, the assist current Ia is reduced by the switch-back current fade characteristic 104 shown as an example in FIG. 5, and the return of the steering wheel 12 is promoted. However, when the steering wheel 12 is kept in a state where the estimated steering angular velocity θsc ′ is substantially zero (during the steering), the switching current fade shown in the switching current fade characteristic 104 in FIG. 5 described above. When the process is executed, the assist time during steering is shortened.

  When the driver desires to hold the steering wheel and the SAT is large, when the switchback current fading process is executed, the driver needs to further increase the steering holding force applied to the steering wheel 12, so the assist is continued. Thus, it is preferable to reduce the steering force by the driver at the time of steering.

  Therefore, in the first embodiment, a function of reducing the driver's steering force at the time of steering, in other words, continuing an appropriate assisting force at the time of steering is realized.

  Next, the steering assist function according to the first embodiment will be described with reference to the flowcharts of FIGS. 7 and 8 and the characteristic diagram of FIG.

The flowchart of FIG. 7 shows the detailed process of the “ switchback current fade process” in step S9 in the flowchart of FIG. 3, and the flowchart of FIG. 8 shows the “ steering cancellation process in step S9d of the flowchart of FIG. The detailed processing is shown. Further, in the characteristic diagram of FIG. 9, for the convenience of understanding, the portion of the first quadrant is enlarged and displayed in the characteristic diagram of FIG.

  When the estimated steering angular velocity θsc ′ becomes equal to or smaller than the threshold steering angular velocity θsc′th = 7.2 [deg / s] in the determination in step S8 described above, the switchback current fade process is started in step S9. . Therefore, in step S9a in FIG. 7, it is determined whether or not the switchback current fade process is being performed. If the switchback process is being performed, the switchback current fade process described with reference to FIG. The process of automatically and gradually attenuating the assist current Ia to zero value is continued in a time of about 1 second.

  In the first embodiment, while the switchback current fade process is continuing, it is monitored in step S9b whether or not the steering continuation determination condition is satisfied. Here, the steering continuation determination condition is a threshold steering angular velocity θsc′tha (for example, θsc′tha = 3.6 [deg / s), which is a relatively small value at which the steering angular velocity θsc ′ is regarded as continuing steering. ]) It is in the state of the following value, and the time (steering duration time) tk (timed by the time measuring unit 85) from the start of the switchback current fade process in step S9a is predetermined. It is determined by whether or not the time Tkth (threshold steering continuation time is shorter than a predetermined time of about 1 second, which is the predetermined time of the switchback current fading process), for example, whether Tkth = 500 [ms] is continued { (Θsc ′ ≦ θsc′tha) continues for a predetermined time Tkth or more}.

  When the determination in step S9b is affirmative, that is, when Tkth = 500 [ms] has elapsed since the start of the return current fade process based on the return current fade characteristic 104 at the coordinate point 107 in FIG. And the estimated steering angular velocity θsc ′ is a value equal to or less than a threshold steering angular velocity θsc′tha = 3.6 [deg / s] that is regarded as steering retention (see coordinate point 108 in FIG. 9), step S9c. , It is determined that the steering is being continued, and the switchback current fade process is interrupted.

  At this time, the time measurement for one second determined in the switching back current fading process in the time measuring unit 85 is interrupted at the time point (coordinate point 108) when the above-mentioned threshold keeping duration Tkth = 500 [ms] is measured (FIG. 5). 9).

  The assist current Ia at this point in time during the switchback current fade process (when the determination in step S9b becomes affirmative and the process in step S9c is interrupted) is maintained at the coordinate point 108 (θsc2, Iak) shown in FIG. The rudder assist current Iak is set.

  Due to the interruption based on the steering continuation determination of the switchback current fade process, the assist current Ia is retained in the storage unit 78 as the steering assisted current Iak in step S9c. Further, the estimated steering angle θsc at this time is held in the storage unit 78 as the estimated steering angle θsc2.

  In the first embodiment, the interruption process based on the steering continuation determination of the switchback current fade process is executed at the position of the coordinate point 108 on the switchback current fade characteristic 104 shown in FIG.

  The steering assist current Iak at the coordinate point 108 is basically supplied to the motor 24 until the steering cancellation condition described in the next step S9d is satisfied, and assists the driver's steering state. By assisting in this way, it is possible to reduce the steering force when the driver steers the steering wheel 12 (when the vehicle turns with a constant radius of curvature).

  Next, a cancellation process of this interruption process, in other words, a steering cancellation process is executed in step S9d.

  FIG. 8 shows a detailed flowchart of the steering hold releasing process in step S9d.

  In step S9d1, it is determined whether or not the switchback current fade process is interrupted due to establishment of the steering continuation determination condition.

  In the first determination, since the interruption process of the switchback current fade process in step S9c is executed, the determination in step S9d1 becomes affirmative. Next, in step S9d2, whether or not the steering cancellation condition is satisfied. Is determined.

The condition for determining whether or not to hold the steering hold condition is that the estimated steering angle θsc gradually decreases from the estimated steering angle θsc2 at the coordinate point 108 (the steering wheel 12 is returned to the neutral position), and the return determination steering angle Δθsc is For example, when Δθsc = 10 [deg] or more (θsc ≦ θsc2−Δθsc) , it is determined that the steering state of the steering wheel 12 by the driver is released.

  When this determination is established at the position of the coordinate point 110 in FIG. 9, the switching current fading process is resumed in step S9d3, so that the assist current is automatically set as indicated by the dashed line in FIG. Ia is reduced.

  As described above, according to the first embodiment described above, when an abnormality of the torque detection unit (the torque sensor 20, the torque detection circuit 72, and the harness 91 therebetween) is detected by the abnormality detection unit 80, the rotation angle is detected. The motor 24 is driven by the base assist current Ia calculated from the base assist current characteristic 102 based on the estimated steering angle θsc based on the rotation angle θr of the rotor 23 of the motor 24 detected by the resolver 58 as a unit. At this time, a threshold steering angular velocity θsc′th (= 7.2 [deg] where the absolute value | θsc ′ | of the estimated steering angular velocity (rotor rotational angular velocity) θsc ′ calculated based on the rotation angle θr of the rotor 23 is a predetermined value. / S]) is a process of reducing the base assist current Ia for driving the motor 24 when the following condition is reached (see the coordinate point 107 in FIGS. 5 and 9). After starting the current fading process at the time of switching back and starting the current fading process at the time of switching back, the situation where the absolute value | θsc ′ | of the estimated rotational angular velocity θsc ′ is a predetermined value or less is a predetermined time or less. (In the above example, the threshold steering continuation time Tkth = 500 [ms]) When continuing, as indicated by the coordinate point 108, the switching-back current fading process, which is a process of reducing the assist current Ia, is interrupted. Since it did in this way, suitable assist force can be provided at the time of what is called steering.

At the time of steering assist when the reduction of the assist current Ia is stopped , the estimated steering angle θsc is gradually decreased (the steering wheel 12 is returned to the neutral position), and the return amount of the estimated steering angle θsc is When the return determination steering angle Δθsc [deg] (predetermined value) is reached (see coordinate point 110), that is, when the first condition for holding the steering release condition is satisfied, the steering state by the driver Since it is determined that has been released and the interruption of the process of reducing the current is resumed, the assist force can be reduced when the steering is no longer necessary.

  Further, at the time of the steering assist when the reduction of the assist current Ia is stopped, the absolute value of the estimated steering angular velocity (estimated rotational angular velocity) θsc ′ becomes a value equal to or higher than the steering cancellation determination threshold steering angular velocity θsc′th1, which is a predetermined value. In this case, that is, even when the second condition for canceling the steering hold condition is satisfied, the interruption of the current fading process at the time of switching back is resumed, so that the assist force is reduced when the steering is no longer necessary. be able to.

[Second Embodiment] (Overcut control function)
As described above, the assist amount (assist characteristic) is determined according to the estimated steering angle θsc, and the fade is adjusted by the current fading process at the time of cutting, the current fading process at the time of switching back, the steering determination process, and the like. For example, after determining the assist amount (assist characteristic) on a high μ road (μ is a friction coefficient), if the steering operation is performed on a low μ road having a different balance (balance) of the required assist amount with respect to the estimated steering angle θsc, May cut too much. As described above, the balance between the estimated steering angle θsc and the necessary assist amount is closely related to the magnitude of the friction coefficient μ of the road surface.

Therefore, in the second embodiment, at the time of incision current fade processing in step S 7, cut too much at the low μ road, based on considerations of the may be limiting the assist amount became excessive state, the motor control The unit 84 calculates a ratio Rm (referred to as a motor rotation speed reduction ratio or a motor rotation speed reduction ratio) corresponding to the motor rotation speed N [rps] of the motor 24 with respect to the assist current Ia.

  FIG. 10 shows a characteristic (motor rotational speed reduction characteristic) 112 of the motor rotational speed reduction ratio Rm according to the second embodiment.

  Until the motor rotational speed N is N = 0 to 2 [rps] (θsc ′ = 0 to 36 [deg / s] at the estimated steering angular speed θsc ′), the value of the motor rotational speed reduction ratio Rm is 1 (no reduction). )), And the motor rotational speed N is N = 2 to 7 [rps] (θsc ′ = 36 to 126 [deg / s]), the value of the motor rotational speed reduction ratio Rm is proportionally reduced from 1 to 0. It is a characteristic.

  The motor rotation speed reduction ratio Rm is a coefficient for detecting and correcting the estimated steering angular speed of the steering wheel 12 of the driver and reducing and correcting the assist current Ia in order to suppress excessive cutting when the estimated steering angular speed is large. .

  Note that when the motor rotation speed reduction ratio Rm is reduced by the motor rotation speed reduction characteristic 112 in FIG. 10, there is a possibility that a desired assist force cannot be ensured during low-speed traveling that requires assistance. For the purpose of preventing an increase in the horizontal axis argument of the motor rotation speed reduction characteristic 112, that is, the motor rotation speed N, as the Vs becomes lower, the motor rotation speed N as the horizontal axis argument is shown in FIG. Control is performed so that the vehicle speed ratio Rv is applied. The vehicle speed ratio Rv is, for example, a value of about 0.25 when the vehicle speed Vs is about Vs = 10 [km / h] from the stop state, and is 0 when the vehicle speed Vs is about 10 to 50 [km / h]. It is set to a characteristic (vehicle speed characteristic) 114 that increases from approximately 0.9 to 1 (no reduction) when the vehicle speed Vs = 50 to 80 [km / h]. Yes.

That is, as schematically shown in FIG. 12, the motor control unit 84 determines the vehicle speed ratio Rv with reference to the vehicle speed characteristic 114 of FIG. 11 with respect to the vehicle speed Vs, and then sets the vehicle speed to the motor rotational speed N [rps]. A motor rotation speed after correction obtained by multiplying the ratio Rv by the multiplier 111 (hereinafter referred to as a correction motor rotation speed) Ns [rps], with reference to the motor rotation speed reduction characteristic 112 of FIG. decide.

  For the base assist current Ia (Ia ← Ia × Rm) after correction of the value obtained by multiplying the base assist current Ia obtained by the base assist current characteristic 102 by the motor rotation speed reduction ratio Rm, the above-described cutting current fade process is performed. Do.

  By controlling in this way, it is possible to achieve both suppression of excessive cutting at high vehicle speeds and securing of assist force at low vehicle speeds. As a result, it is possible to perform assist control capable of achieving both a high μ road and a low μ road.

  Even when the steering angle θs of the steering wheel 12 is cut too much due to an input of disturbance from the wheels such as the steered wheels 16, it is possible to suppress overcutting by using the motor rotation speed reduction ratio Rm. Thus, the so-called disturbance tolerance (disturbance toughness) can be secured.

  As described above, according to the second embodiment described above, the torque Tr generated in the steering wheel 12 as an operator operated by the driver to steer the vehicle and the steering system 18 of the vehicle is detected. A torque sensor 20 as a torque detection unit, a vehicle speed sensor 86 as a vehicle speed detection unit for detecting the vehicle speed Vs of the vehicle, a motor 24 for applying assist torque to the output shaft 42 as a rotating shaft of the steering system 18, and steering A resolver 58 as a rotation angle detection unit for detecting the rotation angle of the system 18, a motor control unit 84 for controlling a current (assist current) Ia for driving the motor 24 based on the torque Tr detected by the torque sensor 20, An electric power steering apparatus 10 comprising: an abnormality detection unit 80 that detects whether an abnormality has occurred in the torque sensor 20 or the like; A storage unit 78 that stores the relationship between the rotation angle θr detected by the Luba 58 and the current Ia that drives the motor 24 as the characteristic 102, and the motor control unit 84 uses the abnormality detection unit 80 to detect abnormality of the torque sensor 20 and the like. Is detected, the motor 24 is driven on the basis of the rotational angle θr detected by the resolver 58 and the characteristic 102. When the motor 24 is driven, an estimated steering angular velocity (rotational angular velocity) θsc ′ calculated based on the rotational angle θr is driven. The motor rotation speed reduction ratio Rm (see FIG. 10) is introduced and controlled so as to reduce the current Ia for driving the motor 24 as the motor rotation speed N corresponding to.

  According to the second embodiment, when an abnormality such as the torque sensor 20 is detected by the abnormality detection unit 80, the motor 24 is driven based on the rotation angle θr detected by the resolver 58 and the characteristic 102, and is driven. In this case, since the motor rotation speed N {estimated steering angular speed (rotational angular speed) θsc '} calculated based on the rotational angle θr is controlled to decrease the current Ia for driving the motor 24, the torque sensor 20 is abnormal. In this case, an appropriate assist force can be applied while preventing excessive cutting in the cutting direction.

  In this case, the motor control unit 84 reduces the motor rotation speed N detected by the resolver 58 so as to decrease as the vehicle speed Vs becomes lower than a predetermined vehicle speed (approximately 80 [km / h] in the example of FIG. 11). Correction is made by the ratio Rv, and the motor 24 is driven based on the corrected motor rotation speed Ns (see FIG. 12) and the characteristic 102. In other words, as the vehicle speed Vs becomes lower than the predetermined vehicle speed, the motor 24 is driven. Since the motor 24 is driven using the corrected motor rotational speed Ns (corrected rotational angular speed) that decreases the motor rotational speed N {estimated steering angular speed (rotational angular speed) θsc '} as an argument of the current Ia to be driven. It is possible to secure an assist force at a predetermined vehicle speed or less where a steering force is more necessary.

  According to the second embodiment, even when the torque sensor 20 or the like fails and the steering torque Tr cannot be detected, the motor rotation speed N of the motor 24 {estimated steering angular velocity (rotational angular velocity) θsc '} The steering assist force by the motor 24 can be applied in both the cutting direction and the return direction, and in particular, assisting as the motor rotation speed N {estimated steering angular velocity (rotational angular velocity) θsc '} increases in the cutting direction. Since the force is controlled to be small, an appropriate assist force can be applied while preventing excessive cutting.

[Third embodiment] (Steering force reduction function when switching back to an extremely low speed traveling region)
When the assist current Ia becomes zero by the switchback current fade process based on the switchback current fade characteristic 104 described with reference to FIG. 5 or FIG. 9, the estimated steering angle θsc is not yet zero. When the estimated steering angle θsc in the right direction remains (in the example of FIGS. 5 and 9, the remaining estimated steering angle θscr having a different value remains), in other words, the switchback angle in the left direction remains. When the assist current Ia in the right direction (cutting direction) becomes zero or close to zero in the state, the vehicle speed Vs is Vs = Vs1 = 20 [km / h] or less, and the steering wheel is driven by SAT. The force to return 12 (steering system 18 ) to the straight traveling direction (neutral position) is weak, and a large amount of steering force (steering torque) for switching back by the driver is required.

  Therefore, in the third embodiment, when the assist current Ia becomes zero by current fading processing based on the switching back current fade characteristic 104, the estimated steering angle θsc is not yet zero, but the right direction is estimated. Even when the steering angle θsc remains (also referred to as a residual estimated steering angle θscr), it is possible to apply the assist force on the return side to the steering wheel 12 (steering system 18).

  Next, referring to the flowchart of FIG. 13 and the characteristic diagrams of FIGS. 14 and 15, the steering force reduction function at the time of switching back to the extremely low speed traveling area according to the third embodiment will be described.

  Therefore, in step S10 of FIG. 13 after the process of step S9 of FIG. 3, whether or not the switchback current fade process based on the switchback current fade characteristic 104 is completed by the motor control unit 84 is determined by the value of the assist current Ia. Determined.

  That is, when the assist current Ia becomes substantially zero (Ia≈0) and the determination in step S10 becomes affirmative, and the estimated steering angle θsc remains more than the dead zone corresponding steering angle θd (FIG. 5 example, FIG. In the nine examples, the remaining estimated steering angle θscr remains.) In step S11, the vehicle speed Vs is lower than the extremely low vehicle speed Vs1 (Vs1≈20 [km / h]) by the motor control unit 84 (Vs <Vs1). ) Or not. The extremely low vehicle speed Vs1 may be set to a value within 5 to 20 [km / h] depending on the vehicle type.

  If not below (step S11: NO), the SAT is activated, so the process returns to step S1 again. At this time, after steps S1, S2, S3, S4 (YES), step S5, and step S6 (NO), the process returns to the determination of step S10 again.

  On the other hand, when the vehicle speed Vs is lower than the extremely low vehicle speed Vs1 and the determination in step S11 is affirmative, in step S12, the estimated steering angle θsc = θsc3 (referred to as a residual return angle) is set as the reference angle θf [deg. ] (See FIG. 14).

Next, in step S13, in the same manner as in steps S1 to S3, a switchback estimated steering angle (also referred to as switchback rotation angle or switchback angle) θsc in the switchback direction is calculated.

  Next, in step S14, the base assist current characteristic 102 is referred to, and the switchback-side assist current Ia corresponding to the switchback estimated steering angle θsc is calculated.

  Next, in step S15, it is compared and determined whether or not the absolute value | θsc | of the estimated steering angle θsc is a value that passes the threshold estimated steering angle θsc4 (see FIG. 15). As an example, the threshold estimated steering angle θsc4 is set to θsc4≈30 [deg].

  In a range in which the determination in step S15 is negative (step S15: NO), the assist current Ia in the switchback direction (calculated in step S14) along the characteristic 120 shown by the one-dot chain line in FIG. Is driven.

  On the other hand, if the determination in step S15 is affirmative, then, in step S16, the center ratio (neutral position return ratio) Rn indicated by the characteristic 118 in FIG. 15 is calculated in step S14 before correction. A corrected assist current Ia (Ia ← Ia × Rn) obtained by multiplying the current Ia is calculated.

  In other words, the center ratio Rn exceeds the neutral position (center) so as not to apply the assist force, as shown by the characteristic 123 in FIG. 14, the switchback estimated steering angle θsc is calculated from the threshold estimated steering angle θsc4. This is the ratio (characteristic) that can be applied to the uncorrected assist current Ia in order to gradually reduce the assist current Ia to zero when the absolute value becomes smaller.

  Next, in step S17, the motor 24 is driven by the assist current Ia (characteristic 120) calculated in step S14 described above or the assist current Ia (Ia ← Ia × Rn) (characteristic 123) corrected in step S16.

  When the steering angle of the steering wheel 12 reaches the neutral position at the time of the switch back, the base assist characteristic 102 can appropriately assist the subsequent cut direction and switch back direction by resetting the switch back rotation angle θsc. It can be carried out.

  If the control is performed as in the flowchart of FIG. 13, even when the assist current Ia in the cutting direction is close to the zero value in the state where the switchback angle remains (residual switchback angle θsc3), Assist is possible, and excessive assistance to the switchback side is prevented.

As described above, according to the third embodiment described above, the torque for detecting the torque Tr generated in the steering wheel 12 as an operator operated by the driver to steer the vehicle and the steering system 18 of the vehicle. A torque sensor 20 as a detection unit, a vehicle speed sensor 86 as a vehicle speed detection unit that detects a vehicle speed Vs of the vehicle, a motor 24 that applies assist torque to an output shaft 42 as a rotation shaft of the steering system 18, and the steering system 18 An electric power steering system comprising: a resolver 58 as a rotation angle detection unit that detects the rotation angle θr of the motor; and a motor control unit 84 that controls a current Ia that drives the motor 24 based on the torque Tr detected by the torque sensor 20. The abnormality detection unit 80 that detects whether or not an abnormality has occurred in the torque sensor 20 or the like, and the resolver 58 are detected. A storage unit 78 that stores the relationship between the rotation angle θr and the current Ia that drives the motor 24 as the characteristic 102, and the motor control unit 84 detects when an abnormality such as the torque sensor 20 is detected by the abnormality detection unit 80. At the time of switching back when the steering angle of the steering wheel 12 changes toward the neutral position, the assist current Ia in the cutting direction is zero when the switching back angle remains (remaining estimated steering angle θscr = residual switching back angle θsc3). When it is close to the value (step S10: YES), the rotation angle θr detected by the resolver 58 is used as the reference angle θf to detect the return rotation angle θsc, and the inversion is performed based on the return rotation angle θsc and the characteristic 102. The motor 24 is driven in a reverse direction opposite to the direction (current fading process may be performed at this time).

  As described above, the estimated steering angle θsc detected by the resolver 58 when the assist current Ia in the cutting direction becomes close to the zero value in the state where the remaining switchback angle θsc3 remains, the switchback rotation angle θsc as the reference angle θf. Since the motor 24 is driven in the reversing direction opposite to the incising direction based on the reversing rotation angle θsc and the characteristic 102, the operation angle of the steering wheel 12 approaches the neutral position. Assist is possible, and the steering force of the steering wheel 12 by the driver on the switchback side can be reduced, and the steering wheel 12 can be easily returned to the vicinity of the neutral position.

  In this case, since the driving of the motor 24 at the time of switching back is enabled when the vehicle speed Vs is equal to or lower than the extremely low vehicle speed Vs1, which is a predetermined vehicle speed, switching is performed even when the SAT (self-aligning torque) is weak. The driver's steering force on the side can be reduced.

  It is preferable to multiply the drive current Ia of the motor 24 at the time of switching back by a predetermined coefficient corresponding to the steering performance of the vehicle. Since the steering performance of the vehicle varies depending on the magnitude of the load for each individual vehicle (vehicle front axle load), the vehicle steering performance can be obtained by multiplying the driving current Ia of the motor 24 by a coefficient corresponding to the steering performance of the vehicle. Optimal assistance according to the situation becomes possible. When the vehicle front axle weight is larger than the standard front axle weight, a coefficient larger than 1 is preferable, and when it is smaller, a coefficient smaller than 1 is preferable. The coefficient multiplication process may be performed as a correction process when calculating the current Ia in step S14.

  As described with reference to the center ratio Rn in FIG. 15, the current Ia of the motor 24 is controlled to decrease as the steering angle of the steering wheel 12 corresponding to the switchback angle θsc approaches the neutral position. In the vicinity of the neutral position, the assist current Ia has a substantially zero value, and over-assist can be avoided.

  In addition, when the steering angle of the steering wheel 12 reaches the neutral position at the time of switching back, the assist in the subsequent cutting direction is reset by resetting the increased switching back rotation angle θsc so that the base assist shown in FIG. The characteristic 102 can be appropriately performed.

[The steering force of the driver according to the embodiment and the first to third examples, the steering force of the driver when the torque sensor 20 is normal, and the steering force when there is no assist control (steering force by manual steering) Schematic comparison]
For example, when a steering operation of the steering wheel 12 is performed such that the vehicle speed Vs turns right at an intersection at a speed of about Vs = 30 [km / h], the torque sensor 20 of the electric power steering device 10 is normal (step S21). In the normal control of FIG. 16, the steering force (steering torque) of the driver with respect to the steering angle θs [deg] of the steering wheel 12 is the steering torque characteristic (steering force characteristic) 132 indicated by the one-dot chain line at the lowest level in FIG. As shown.

  On the other hand, when the torque sensor 20 becomes abnormal and the provisional assist control is not performed, that is, in the case of manual steering, as shown in the steering torque characteristic 130 indicated by the broken line in FIG. (Steering torque) is required to be about four times the steering torque characteristic 132 when the steering torque is normal (when the estimated steering angle θsc is about 150 [deg]).

On the other hand, provisional assist control (also referred to as resolver assist control) using the resolver 58 and the like according to the above-described embodiment and Examples 1 to 3 (the steering angle sensor 19 if the steering angle sensor 19 is normal). According to this, the steering torque characteristic 134 can be set to increase the steering force (steering torque) about 2.5 times the steering torque characteristic 132 in the normal case. In other words, the steering torque characteristic 134 by the resolver assist control has a larger range of the estimated steering angle θsc that exceeds the dead zone corresponding steering angle θd as compared with the steering torque characteristic 130 of the manual steering when the steering assist control is not performed. Thus, the assist force can be reduced by approximately 30%.

  In addition, this invention is not restricted to embodiment mentioned above, 1st Example-3rd Example, Of course, based on the description content of this specification, various structures can be taken.

DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus 18 ... Steering system 20 ... Torque sensor 24 ... Brushless motor 25 ... Rotating shaft 58 ... Rotor rotation angle detection part 74 ... Steering angular velocity detection part 78 ... Memory | storage part 80 ... Abnormality detection part 82 ... Vehicle stop state Detection unit 84 ... motor control unit 86 ... vehicle speed detection unit 101, 102 ... characteristic Ia ... current Iamax ... current limit value Rc ... continuous steering reduction ratio Rm ... motor rotation speed reduction ratio Rn ... center ratio Rv ... vehicle speed ratio Ta ... assist torque Tr ... Torque Vs ... Vehicle speed θd ... Dead zone compatible steering angle θf ... Reference angle θr ... Rotation angle (motor electrical angle) θre ... Motor electrical angle θrm ... Motor mechanical angle θs ... Steering angle θsc ... Estimated steering angle (switchback estimated steering angle) )
[theta] sc3 ... residual return angle [theta] scth ... threshold steering angle [theta] s '... steering angular velocity [theta] sc' ... estimated steering angular velocity [theta] sc'th ... threshold steering angular velocity θsc'th1 Steering angle

Claims (5)

An operator that the driver operates to steer the vehicle;
A torque detector for detecting torque generated in the steering system of the vehicle;
A vehicle speed detector for detecting the vehicle speed of the vehicle;
A motor for applying assist torque to the rotating shaft of the steering system;
A rotation angle detector for detecting a rotation angle of the steering system;
A motor control unit for controlling a current for driving the motor based on the torque detected by the torque detection unit;
An electric power steering apparatus comprising:
An abnormality detection unit that monitors and detects the torque signal detected by the torque detection unit to determine whether or not an abnormality in which the torque cannot be detected has occurred in the torque detection unit ;
A storage unit that stores, as a characteristic, a relationship between the rotation angle detected by the rotation angle detection unit and the current that drives the motor, and the motor control unit includes:
When an abnormality of the torque detection unit is detected by the abnormality detection unit, an assist current in the cutting direction with the switchback angle remaining at the time of switchback in which the steering angle of the operation element changes in a direction approaching a neutral position When the rotation angle is near the zero value, the rotation angle detected by the rotation angle detection unit is used as a reference angle to detect the return rotation angle,
The electric power steering apparatus, wherein the motor is driven based on the return rotation angle and the characteristic. The electric power steering apparatus according to claim 1,
The electric power steering device according to claim 1, wherein the driving of the motor at the time of switching back is effective when the vehicle speed is equal to or lower than a predetermined vehicle speed. In the electric power steering apparatus according to claim 1 or 2,
An electric power steering apparatus characterized by multiplying a drive current of the motor at the time of switching back by a predetermined coefficient corresponding to the steering performance of the vehicle. In the electric power steering device according to any one of claims 1 to 3,
The electric power steering device according to claim 1, wherein the current of the motor is reduced as the steering angle of the operating element approaches a neutral position at the time of switching back. In the electric power steering device according to any one of claims 1 to 4,
When the steering angle of the operation element reaches a neutral position at the time of the switchback, the switchback rotation angle is reset.

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